The present invention relates to jack stands for aircraft and, more specifically, to a portable adjustable height tail stand which attaches to the tail skid of an aircraft and includes a warning system which notifies persons working on the aircraft that the tail stand is in danger of damaging the aircraft.
Aircraft, while on the ground, frequently require the use of a tail stand to prevent the aircraft from sitting down on its tail and damaging the fuselage of the aircraft. Most aircraft today are the tricycle gear design having two main gears and a nose gear, with the center of gravity of the aircraft located between the main gear of the aircraft and the nose gear. When a freight or passenger aircraft is being loaded, tail stands are always set in place so that if the center of gravity of the aircraft, due to the freight being loaded, momentarily shifts behind the main gears, the aircraft will attempt to sit down on its tail, which the jack tail stand prohibits. This use of such a tail stand is shown in the patent to Weiland et al., U.S. Pat. No. 3,051,419. Once aircraft are fully loaded, it is quite critical that the placement of the freight has not moved the overall center of gravity of the aircraft outside the flight envelope, which of course would render the aircraft dangerous to fly.
Other uses of the tail stands in aircraft for which the present invention is being used involve the construction stages of the aircraft and the maintenance thereof. With a single engine aircraft, when the engine is removed, the center of gravity (CG) of the aircraft shifts behind the main wheels and the aircraft must be supported by the tail stand. One manner in which this imbalance problem is handled would be by attaching a heavy weight to the nose of the aircraft once the engine is removed to retain the C.G. forward of the main wheels. Frequently during construction and maintenance, aircraft are elevated off their wheels by three hydraulic jacks that lift the aircraft at three hard points, one under each wing, and one at the nose. In this lifted position of the aircraft, the retractable landing gears can be cycled up and down for adjustment and maintenance as required.
During the construction of new aircraft, frequently the aircraft is held in an elevated position off the floor at the three points above mentioned, with the tail stand in place. The addition of various parts of the aircraft, such as engines and temporary testing equipment, may cause the center of gravity to shift behind the main wheels, which would cause the plane to tilt back on its tail stand.
A further condition the present invention is concerned with is when the aircraft is being lowered off the jacks, sometimes the tail stand has not been removed and as the aircraft is lowered, serious damage can be caused to the tail area of the empennage by forgetting to remove the tail stand. With the present invention, as soon as weight is transferred to the tail stand, a horn is activated.
Tail stands on aircraft have been widely used over the years such as in the patent to Weiland et al., U.S. Pat. No. 3,051,419, wherein a cargo plane is loaded from the rear which causes a temporary shifting of the center of gravity as the plane is loaded.
The patent to Evans, U.S. Pat. No. 4,378,098, illustrates another form of jack stands that are positioned both forward and aft on both sides of the aircraft during the loading and unloading of freight.
The patent to Pugh et al., U.S. Pat. No. 4,042,135, teaches a turnover moment sensing device for a crane which functions through strain gauges which senses the turnover moment of the crane caused by the offset nature of the load and the degree of extension. In essence, this warning device notifies the operator before the crane tips over through the use of strain gauges placed in the front axle.
The patent to Long, U.S. Pat. No. 5,445,352, teaches a portable telescoping stand for supporting pickup truck campers, which includes a theft warning device which senses when weight is removed from the stand which sets off an alarm.
The present invention is used in combination with newly constructed aircraft during various lifting and lowering stages during assembly and various testing stages. Those would include lifted stages where the aircraft was supported on jacks and the various landing gears were free to extend and retract in a simulated flight condition.
The tail stand of the present invention attaches to the tail skid of the aircraft or is positioned under the empennage section as a cradle, shaped to the under surface of the empennage. The tail stand prevents the tail of the aircraft from ever coming in contact with the ground and damaging the surrounding empennage area.
With the warning system of the present invention, if the tail of the aircraft begins to settle by reason of either lowering the aircraft from its jacks or sufficient aft center of gravity shift, the warning horn notifies the workers through a loud air horn that the tail stand is in danger of damaging the aircraft with any further lowering of the lifting jacks which are lowering the aircraft.
Therefore, the principal object of the present invention is to provide an aircraft tail stand with a very simple warning device when the tail stand is in danger of damaging the aircraft.